Effect of Canola Size on Winter Survival

Several canola producers across the state are wondering if their canola is either “too big” or “too small” going into the winter months. We often hear that winter canola needs to be roughly “the size of a dinner plate” to survive the upcoming winter months, but is this the correct size? Canola overwinters in the rosette growth stage and has the ability to tolerate cold temperatures as low as 0 degrees Fahrenheit provided that exposure is not excessive. This stage of growth is made up of larger older leaves that surround the base and new smaller leaves at the center which surrounds the all-important crown.

For optimum winter survival, researchers at Kansas State University recommend that winter canola plants should have 5 to 8 true leaves, equal to about 6 to 12 inches of fall growth. Canola plants that are too large (typically 20 inches or more) or those plants where the crown has grown above the soil surface can become susceptible to exposure and winter kill. There are several reasons that can contribute to excessive stem elongation in the fall (Table 1). It is important not to confuse stem elongation with bolting. Bolting is when the plant elongates and begins to develop buds and ultimately flowers later in the growing season.

Causes of Excessive Fall Stem Elongation

Stem elongation in the fall — not to be confused with bolting, (i.e. stem elongation with visible flowering structures) — may occur because:

  • the crop was planted too early
  • the crop was seeded at higher-than-optimal plant populations
  • excessive soil fertility is present (particularly nitrogen)
  • an unusually warm fall persists
  • selection of a poorly adapted cultivar
  • a combination of any of these factors*
Plant growth site going into winter

Figure 1. Variety Claremore

Snow cover can help provide a layer of protection against extreme cold temperature. The Waterville Plateau received a blanket of snow on November 30th (Figure 1). At our WSU Canola Variety Trials across the state, plant counts are taken in the Fall and Spring to determine which varieties are best suited for winter survival within those individual regions.

Winter Survival and Stand Establishment are two of the many topics that will be part of our oilseed workshops scheduled for January 22 in Hartline, WA; January 24 in Richland, WA; and January 25 in Colfax, WA.

* Source: Mike Stamm and Ignacio Ciampitti, Kansas State University Extension, as published in No-Till Farmer.

For questions or comments, contact Dale Whaley by email at dwhaley@wsu.edu or by phone at 509-745-8531.
Washington State University